The invention relates to a chain belt of the type used in continuously variable cone-pulley transmissions of vehicles, and it further relates to a method of manufacturing the chain belt as well as an apparatus for performing the method.
Chain belts of this type have links that are connected to each other by coupling members. Examples are known, e.g. from DE 35 26 062 and DE 44 15 838. The links in the chain belt are normally arrayed in transverse rows of multiple links, where each row of links is pivotally connected to the next by coupling members, typically in the form of transverse pins passing through openings in the links. To secure the links, i.e., to keep them from falling off the ends of the coupling members, the foregoing reference patents propose metallic retainer elements to be attached to the coupling members by laser welding.
According to DE 35 26 062, the metallic retainer elements are made by punching the pieces from sheet metal band material. They can also be made from rings of metal band that are subsequently cut open. The manufacture of the retainer elements from band material consumes a considerable amount of excess material beyond what is actually required for the retainer elements themselves. Due to the nature of the cutting process, a large portion of the material is wasted as scrap. Another disadvantage is that, due to the punching forces, the metal elements become warped and that the cutting process can cause undesirable chips and burs that are detrimental to the quality of the end product.
If the metal retainers are laser-welded to the coupling members, the manufacturing process requires a precise alignment of three elements in order to ensure a secure attachment of the retainer element. The coupling member has to be held in a fixed position, the retainer element has to be precisely located on the coupling member, and the laser beam has to be focused at the exact spot of the coupling member and/or the retainer element. The manufacturing process has to be designed with built-in assurance to keep these factors under control. This adds to the process time and thus reduces the throughput rate of the manufacturing process.
As a further observation, the one-sided exposure of the retainer element and/or coupling member to the laser beam causes a one-sided deformation of the retainer element, so that the retainer piece is attached in a distorted condition in the welding process. This reduces the holding strength of the attachment and the quality of the attachment of the retainer element in general.
It is therefore the object of the present invention to provide a chain belt that belongs to the same type as described above but is based on an inherently less complicated design and can be more reliably controlled in the manufacturing process. In addition, the invention aims to provide a less complicated and less time-consuming manufacturing process. As a further object of the invention, a chain belt is to be provided with retainer elements that can be attached to the coupling members with a superior holding strength. An additional purpose is to reduce the amount of material consumed in manufacturing the chain belt.
According to the invention, the foregoing objective is met by a concept where retainer elements are attached at least to certain individual links and/or coupling members by a resistance-welded bond. In an advantageous embodiment of the invention, the method of resistance/compression welding is used for the attachment. The resistance welding method brings a reduction in the number of parameters that have to be adjusted in the control of the welding process, because the retainer element only has to be placed with a pre-selectable contact force against the part to which it is to be attached. The welding bond can be performed in a simple and reliably controllable operation, e.g., by generating a current flow through a capacitor discharge or other current-producing method.
According to a further concept, the object of the invention can also be attained if the retainer elements are attached at least to certain individual links and/or coupling members by friction welding.
Friction welding, likewise, offers a reduction in the number of parameters that have to be adjusted in the control of the welding process, because the retainer element only has to be pressed with a high contact force against the part to which it is to be attached, accompanied by a rotatory or oscillatory motion of the two parts in relation to each other. This causes the two parts to melt in the contact zone and thereby form the welded bond.
With the embodiments of the invention described above, it is particularly advantageous if the retainer element is a metal part. Particularly suitable is a metal ball. According to the invention, this has the advantage that the retainer elements can be fed to the fastening apparatus as finished individual pieces and, because of their spherical shape, without regard to orientation.
This eliminates the cutting process with its inherent waste of material due to the cut-away scrap portions, and it also eliminates the down time for putting a new roll of sheet metal band in place after the previous roll has been used up. By using retainer elements in the form of finished articles, the time that would otherwise be required for changing the roll can be used productively to increase the throughput rate of the manufacturing process.
There can also be cases where it is practical if the retainer element is a substantially square, cylindrical, hollow-cylindrical, hemispherical or crescent-shaped element, or a cone, a frustum, a segment of a sphere, a sphere with a hole, a ring, or a prismatoid. A retainer element in one of these shapes will be easy to attach to the coupling member or to another element that may be specified by the design of the chain.
The invention further relates to a method of manufacturing a chain belt. According to a first embodiment of the inventive method, the retainer element is positioned into contact with a coupling member with or without applying a force, and the bonding is performed by resistance welding.
According to a further concept within the scope of the present invention, the retainer element is positioned into contact with a coupling member with or without applying a force, and the bonding is performed by friction welding.
According to yet another concept within the scope of the invention, the retainer element is positioned into contact with a coupling member with or without applying a force, and the bonding is performed by ultrasonic welding. In the ultrasonic welding process, one of the parts to be connected is put into a state of ultrasonic vibration by means of a so-called sonotrode, so that the contact zone will melt and the welding bond will be formed.
The invention further relates to an apparatus for performing the method. The apparatus or fixture has a first holder element for holding a coupling member and a second holder element for holding a,retainer element. At least one of the holder elements can be set at a variable position in relation to the other. The holder elements that are used to hold and position the elements that are to be welded together can be tongue-or tweezer-like grippers, vacuum-suction holders, holding devices working by means of vacuum or sub-atmospheric pressure, or holding devices working magnetically.
The novel features that are considered as characteristic of the invention are set forth in particular in the appended claims. The improved apparatus itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawing.